Pulping wood with sodium carbonate-lime solution



Patented June 10, 1952 roLPING oon WITH SODIUM CARBON- ATEeLIME SOLUTION Huguenin Miller, Watervliet, Mich., assignor to Water-vliet Paper Company, Watervliet, Mich, a corporation of Michigan,

; Nol l awin 2 Claims. 1,

This invention relates to improvements in pulping; wood with sodium carbonate-lime solution.

This application is a continuation in part of my application for Letters Patent filed June 30, 1Q43; Serial- No. 492,921, nowabandoned.

The main objects; of this invention are:

First, to provide a process enabling the pulping of deciduous wood or wood chips such for example as aspen or poplar which results in a relatively high yield; of' pulp and one in which the lignin content retained inthe pulp approximates-that of'the wood from which the pulp is ormed;

Second; to provide a process of pulping wood chips which may be] economically practiced on a commercial scale with satisfactorily uniform results and with relatively simple apparatus.

Third, to provide a method of producing a wood pulp which results in a pulp adapted for a wide range oi uses in the manufacture of paper and paperboard products and even for molding purposes without necessitating the addition of sizing and chemical fixitives and purely by mechanical manipulations with standard pulp treating and; paper making equipment. Fourth, to provide a wood pulp which may be used in the manufacture of greaseproof paper and the like without the addition thereto of greaseproofing ingredients by mechanical paper melting treatment only.

Fifth, to provide a wood pulp assaying lignin in a percentage approximately equaling the lignin component of the wood from which the pulp is formed and in which the lignin component is not substantially separated from the fibre -l Sixth to provide a method of producing wood pulp which may, if desired, be bleached and made into paper haying highly desirable properties of streng th' andformation abrasionresistance, and ability to take ink; satisfactorily withoutthe incorporating of sizing materials.

Seventh, to provide awood pulp which may be used in the manufacture of sheets having a high degree of moldability, tensile strength, and highly satisfactory burst and tear characteristics,

Further objects and objects relating to details and economies of the invention will appear from the description to follow. The invention is definedin the claims.

My process of producingpulp is well adapted for the preducing of a pulp having the advantages which I have set forth and others which will appear herein.

Application January 16,1946, SerialNo. 641,641

also be taken into consideration in determining the concentration of the solution-Jor example, old wood, that is, wood that has been cut for some time and becomeweathered, may require a somewhat heavier concentration than is required for the same kind of wood which is relatively freshly cut.

In a highly desirable method'of practicing the process, the wood chips are immersed in the solution in a closed vessel orretort and the retort or vessel heated to bring the temperature of the wood chips substantially above boiling temperature and desirably toabout 10 above the boiling point of water at atmospheric pressure plus the hydrostatic head on the most deeply submerged chips. This temperature with standard types of cookers ranges from 220 F. to 255 F. Very satisfactory results can be accomplished if this temperature is reached in approximately minutes by the introduction of steam, approximately 45 minutes being new regarded by the applicant as minimum. During this heating the vessel or retort is vented at intervals to release the air while maintaining pressure therein. When the chips are heated to the desired temperature the pressure within the vessel or retort is released as rapidly as practical without substantial loss of the impregnating solution due to priming to approximately atmospheric pressure. The chips are allowed to soak for impregnation thereof for approximately 20 minutes or until substantially complete impregnation results duringwhich period of impregnation substantially atmospheric pressure is maintained within the vessel by the admission of air or additional solution as the vessel and contents cool. The chips should be thoroughly impregnated with the sodium carbonate solution as it is the object to thoroughly impregnate the chips in this step.

The period of heating the chips may be shortened with steam of higher pressures but it should be understood that the object in this heating and rapid reduction of pressure is to expel the air from the chips and get them into condition for the entrance of the sodium carbonate solution during the soaking or impregnating period.

excess of unabsorbed sodium carbonate solution is then drawn off from the chips and the same retort or vessel used for the succeeding step. However, it is desirable in commercial practice to use more than one processing retort so that the heated liquor or sodium carbonate solution that is drawn oii can be used for another batch or charge of chips. The solution should, however, be tested and replenished to maintain the desired concentration. Using this heated liquor not only saves material but also saves heat.

This impregnation of the chips is carried on without mechanical fragmentation of the chips. The impregnated chips are then immersed in a water suspension of lime containing lime in excess of the amount required for causticization and to remain in excess throughout the subsequent cooking period and while the chips are so immersed. The amount of excess of lime to meet these several conditions or factors is not material so long an a substantial excess is assured or maintained. Ordinarily lime from about to of the oven dry weight of the wood is employed in the ratio of 150 pounds of hydrated lime to 300 gallons of Water.

The retort or digester or closed vessel is then heated, desirably in commercial practice by direct introduction of steam, to a cooking temperature of approximately 280 F., the cooking being continued for about seven hours to render the fibres readily separable by mechanical means. This is found not to substantially reduce the lignin content of the wood or to free the lignin from the fibres which is a highly important and novel feature of the applicants invention.

The batch or charge is then discharged from the retort or digester and washed. The washing may be expedited by subjecting the chips to an attrition mill. The treatment in the attrition mill at this stage does not reduce the chips to any substantial quantity of individual fibres, such reduction being specifically avoided inasmuch as it would interfere with the removal of sludge. The attrition mill is so adjusted and used that the chips are partially broken so that deposits of sludge in the cracks or recesses thereof are more thoroughly exposed to the washing and facilitate the removal of the sludge. For the highest yield, water only is used in the washing but for some products an acid may be added to the washing water. After the washing, the fibres are mechanically separated and subjected to such beating and stock treatment as may be desired for the particular product, I have found it practical to use a double disk Bauer pulper for reducing the washed material to substantially individual fibers.

A very high yield of pulp results from following the applicants process, ranging generally from approximately 85 to 95%, and the lignin content of the wood processed is but slightly reduced. For example, pulp containing 15.7% lignin has been produced by applicant from aspen chips containing 16.5% lignin. Pulp containing 15.2% lignin has been produced by applicant from poplar chips containing 16.5% lignin.

The time of cooking may be shortened by using higher cooking temperatures but applicant considers it desirable not to exceed 320 F. which is generally regarded as the minimum cooking temperature in the soda process. Where a lighter colored pulp is desired, the pulp may be treated with a solution of aluminum sulphate or dilute acid and then washed. Alkaline hypochlorite solution is suitable for bleaching. However, the Washed pulp may go directly to the beater.

The pulp may be beaten to such degree that it possesses superior properties of strength and rigidity, high resistance to penetration by grease or water and even while beaten to that extent has good drainage characteristics-that is, good performance in the making of sheets.

I am enabled to produce greaseproof paper from the pulp without the addition thereto of sizing or greaseproofing ingredients and by mechanical paper making treatment only.

Papers produced from the unbleached pulp assaying lignin in a percentage approximately equal to the lignin component of the wood, the lignin not being substantially separated from the fibre, has many desirable characteristics in addition to its greaseproofing character. To make it greaseproof, however, the pulp should be properly beaten. A highly desirable printing paper may be produced purely by mechanical paper making treatment without the addition of sizing.

It is found that in the manufacture of corrugated boards with a corrugated ply formed of applicants product, the finished board has several times the normal flat crush resistance of corrugated board using a corrugated strawboard ply. The pulp may be used in molding various objects and the result is a very hard resistant structure.

I do not attempt to point out the various possible uses but I have mentioned these uses to bring out that the pulp produced by my method is desirable for use in the manufacture of light papers such as greaseproof papers, printing papers, heavier papers such as wrapping papers and the like, and for molding purposes, all with desirable results and without the addition of other ingredients.

For the highest yield, it is desirable to use water for washing the cooked pulp without the addition of acid thereto. However, where lower concentration of impregnating solutions have been used of the order of 3 or 4%, the use/ of acid in the washing water may be found helpful in producing greaseproof paper, for example. When the concentration of impregnating solution is above 8% the yield is normally lower but defibering and refining may be made easier and ordinarily the ease of bleaching is improved by the easier defibering.

Paper made from my pulp has highly desira ble burst and breaking length qualities. These vary somewhat as would be anticipated by those skilled in the art with variations in the mechanical paper making treatment but it may be generally said that these tests are in general relatively high as compared to products made from pulp produced by methods now in general commercial practice and receiving the same mechanical paper making treatment. Of course, it will be understood that the applicant has economies which result from being able to produce his products without the addition of sizing and other ingredients commonly used.

Other methods of impregnation could be employed within the scope of my inventionfor example a closed vessel containing wood chips could be evacuated mechanically, with or without impregnating solution present, and then filled with solution under hydrostatic pressure.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent. is:

1. The process of pulping deciduous wood chips, which consists of impregnating the chips with a solution of sodium carbonate having a concentration of approximately 6% by immersing the chips in the solution in a closed vessel, heating in the closed vessel by admission of steam thereto for a period of approximately 90 minutes to raise the temperature of the chips to about F. above the boilin point of water at atmospheric pressure plus the hydrostatic head to which the chips are subject while being heated and venting the vessel at intervals during such heating to release the air therefrom while maintaining pressure therein, and at the end of such chip heating period releasing the pressure within the vessel rapidly to approximately atmospheric pressure, allowing the chips to soak for impregnation at a temperature below boiling temperature for approximately minutes during which period fluid is admitted sufiicient to maintain substantially atmospheric pressure Within the vessel, drawing off the sodium carbonate solution in excess of that impregnating the chips, immersing the impregnated chips in a water suspension of lime containing lime in excess of the amount required for causticizing reaction within the chips of the sodium carbonate impregnating the chips, such excess of lime being sufiicient to react with the sodium carbonate within the chips, and to remain in excess throughout the subsequent cooking period and while the chips are so immersed, cookin the chips for a period of approximately seven hours at approximately 280 F. to render the fibres readily separable by mechanical means Without substantially reducing the lignin content of the wood, and washing in water, and then mechanically separating the fibres.

2. The process of pulping deciduous wood chips, which consists of impregnating the chips with a sodium carbonate solution having a concentration of approximately 3% to 8% by immersing the chips in the solution in a closed vessel, heating the closed vessel for a period to 4 raise the temperature of the chips to about 10 F. above boiling point of water at atmospheric pressure plus hydrostatic head on the submerged chips, rapidly releasing the pressure within the vessel to approximately atmospheric pressure, allowing the chips to soak to substantially complete impregnation thereof, drawing ofi the impregnating solution in excess of that impregnating the chips, immersing the impregnated chips in a water suspension of lime containing lime in excess of the amount required for the causticizing reaction within the sodium carbonate impregnated chips, and maintaining an excess throughout the subsequent cooking period and while the chips are so immersed, cooking the chips for such period and at a temperature in excess of 212 F. but less than 450 F. as to render the fibres readily separable by mechanical means without substantially reducing the lignin content of the wood, and washing, and mechanically separating the fibres.

HUGUENIN MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 878 Holland Aug. 13, 1838 1,138,907 Thickens May 11, 1915 1,672,895 Maignen June 12, 1928 1,803,443 Hildebrandt May 5, 1931 1,849,334 Richter Mar. 15, 1932 1,857,432 Codwise May 10, 1932 1,887,863 Stevenson Nov. 15, 1932 2,169,473 Olsen Aug. 15, 1939 2,228,349 Feldman Jan. 14, 1941 FOREIGN PATENTS Number Country Date 113,503 Australia July 14, 1941 609,002 France May 1, 1926 396,284 Germany May, 30, 1924 502,451 Great Britain Mar. 17, 1939 

1. THE PROCESS OF PULPING DECIDUOUS WOOD CHIPS, WHICH CONSISTS OF IMPREGNATING THE CHIPS WITH A SOLUTION OF SODIUM CARBONATE HAVING A CONCENTRATION OF APPROXIMATELY 6% BY IMMERSING THE CHIPS IN THE SOLUTION IN A CLOSED VESSEL, HEATING IN THE CLOSED VESSEL BY ADMISSION OF STEAM THERETO FOR A PERIOD OF APPROXIMATELY 90 MINUTES TO RAISE THE TEMPERATURE OF THE CHIPS TO ABOUT 10* F. ABOVE THE BOILING POINT OF WATER AT ATMOSPHERIC PRESSURE PLUS THE HYDROSTATIC HEAD TO WHICH THE CHIPS ARE SUBJECT WHILE BEING HEATED AND VENTING THE VESSEL AT INTERVALS DURING SUCH HEATING TO RELEASE THE AIR THEREFROM WHILE MAINTAINING PRESSURE THEREIN, AND AT THE END OF SUCH CHIP HEATING PERIOD RELEASING THE PRESSURE WITHIN THE VESSEL RAPIDLY TO APPROXIMATELY ATMOSPHERIC PRESSURE, ALLOWING THE CHIPS TO SOAK FOR IMPREGNATION AT A TEMPERATURE BELOW BOILING TEMPERATURE FOR APPROXIMATELY 20 MINUTES DURING WHICH PERIOD FLUID IS ADMITTED SUFFICIENT TO MAINTAIN SUBSTANTIALLY ATMOSPHERIC PRESSURE WITHIN THE VESSEL, DRAWING OFF THE SODIUM CARBONATE SOLUTION IN EXCESS OF THAT IMPREGNATING THE CHIPS, IMMERSING THE IMPREGNATED CHIPS IN A WATER SUSPENSION OF LIME CONTAINING LIME IN EXCESS OF THE AMOUNT REQUIRED FOR CAUSTICIZING REACTION WITHIN THE CHIPS OF THE SODIUM CARBONATE IMPREGNATING THE CHIPS, SUCH EXCESS OF LIME BEING SUFFICIENT TO REACT WITH THE SODIUM CARBONATE WITHIN THE CHIPS, AND TO REMAIN IN EXCESS THROUGHOUT THE SUBSEQUENT COOKING PERIOD AND WHILE THE CHIPS ARE SO IMMERSED, COOKING THE CHIPS FOR A PERIOD FO APPROXIMATELY SEVEN HOURS AT APPROXIMATELY 280* F. TO RENDER THE FIBRES READILY SEPARATE BY MECHANICAL MEANS WITHOUT SUBSTANTIALLY REDUCING THE LIGNIN CONTENT OF THE WOOD, AND WASHING IN WATER, AND THEN MECHENICALLY SEPARATING THE FIBERS. 